The present invention relates to a polishing apparatus using a light-load dresser, the load of which is controlled by its own weight in combination with a fluid pressure.
A manufacturing process of a semiconductor wafer utilizes a polishing apparatus for planarizing and mirror-polishing a surface of the semiconductor wafer. FIG. 4 is a perspective view, illustrating a general configuration of such a polishing apparatus. The polishing apparatus shown in FIG. 4 comprises a turntable 100 equipped with a polishing cloth adhered to its upper surface, defining a polishing cloth face 103, a top ring 111 arranged above said turntable 100, with a semiconductor wafer W being held thereto or sucked under vacuum against a lower surface thereof, and a dresser 121 also arranged above said turntable 100 for dressing the polishing cloth face 103.
In a polishing operation, a polishing slurry is supplied from a slurry supply nozzle 105 onto the polishing cloth face 103 of the turntable 100 driven rotationally by a driving shaft 101, while the semiconductor wafer W held by the top ring 111 is compressed against the polishing cloth face 103 for polishing to a mirror-surface.
In such an apparatus, if slurry collects on and clogs the surface of the polishing cloth forming the polishing cloth face 103, deterioration in polishing performance will result. Thus, pure water, as required, is supplied onto the polishing cloth face 103 of the rotating turntable 100 from a supply means (not shown), while the dresser 121 is rotated and compressed against the polishing cloth face 103, thereby preventing slurry from clogging (i.e. regenerating the polishing cloth), and maintaining a working condition of the polishing cloth face 103. In such an apparatus, the dresser 121 serves as a tool for abrading the polishing cloth face 103 slightly by a unit of xcexcm (10xe2x88x926 m) or as a tool-for cleaning the polishing cloth face 103.
FIG. 3 shows a dresser driving mechanism of a pneumatic balance control type according to a conventional technology. As shown in FIG. 3, the conventional dresser 121 has its driving shaft 123 operatively attached to an end portion of a swing arm 125 so as to be moved up and down freely with respect to the swing arm 125, and the entire unit of the mechanism can be swingably moved together with the swing arm 125 upon a swinging motion of a support pole 127 of the swing arm 125. The driving shaft 123 is rotationally driven by a motor 129 through a driving belt 131. Further, a dresser driving cylinder 132 is mounted on the swing arm 125, and pneumatic pipes 135 and 137 are respectively connected to chambers xe2x80x9caxe2x80x9d and xe2x80x9cbxe2x80x9d defined within the cylinder 132 on opposite sides of a piston 133. The upper pneumatic pipe 137 is connected to a three-way electromagnetic valve 139 via a throttle valve 138 for restricting an air flow rate. A pneumatic pipe 137a for supplying compressed air and a pneumatic pipe 137b for exhausting the air are connected to the three-way electromagnetic valve 139; and further the pneumatic pipe 137a is connected to a pressure control unit 141; while the lower pneumatic pipe 135 is connected to a relief valve 147 via throttle valves 143 and 145. The relief valve 147 also functions to control a fluid pressure at a constant level.
The pressure control unit 141 functions to decrease a pressure of the supplied compressed air at a predetermined level, and supplying it to the chamber xe2x80x9cbxe2x80x9d of the cylinder 132, while the relief valve 147 functions to relieve the air gradually from the chamber xe2x80x9caxe2x80x9d of the cylinder 132. The pressure control unit 141 also has a function similar to that of the relief valve 147.
When the dresser 121 is moved up, the compressed air at the predetermined level is supplied through the pneumatic pipe 135 into the chamber xe2x80x9caxe2x80x9d of the cylinder 132 while the chamber xe2x80x9cbxe2x80x9d of the cylinder 132 being in communication with the exhaust pipe 137b through the three-way electromagnetic valve 139. When the dresser 121 is to be moved down, the chamber xe2x80x9cbxe2x80x9d is in communication with the pressure control unit 141 through the three-way valve 139 and the compressed air is supplied into the chamber xe2x80x9cbxe2x80x9d so that the piston 133, and thus the dresser 121, is moved downward. The pressure of the dresser 121 applied to the polishing cloth face 103 of the turntable 100 may be adjusted by controlling a pressure balance of the compressed air supplied into both of chamber xe2x80x9caxe2x80x9d and xe2x80x9cbxe2x80x9d of the cylinder 132.
If the dresser 121 abrades the polishing cloth face 103 of the turntable 121 by a large amount, the polishing cloth face 103 is likely to become worn rapidly and be required to replaced frequently. Thus, preferably the dresser 121 should abrade the polishing cloth face 103 by only a small amount so as to extend the life of the polishing cloth. In addition, if the load applied to the polishing cloth face 103 changes during dressing, amount of abrasion of the polishing cloth face 103 will vary, and the condition on the polishing cloth face 103 will be subject to variation resulting in a serious affection to the ability to polish the semiconductor wafer properly. From that point of view, such a dresser 121 has been desired that can maintain the light-load condition stably and can make an amount of abrasion of the polishing cloth face 103 to be as small as possible and also constant.
However, in the conventional dresser driving mechanism of a pneumatic balance control type described above, two pneumatic circuits consisting of two compressed air supplying systems are used and the load applied to the dresser 121 is determined by the balance in air pressure between the two systems. Therefore, the air pressure in the two systems cannot easily be controlled simultaneously with a high degree of precision, and accordingly, it has been difficult to maintain the dresser 121 in a constant light-load condition stably during dressing.
Further, there have been other problems such that upon moving the dresser 121 down, the relief valve 147 moves out of its operational limit due to very light air pressure applied thereto and which prohibits air relief and results in a failure of the downward movement of the dresser 121. Additionally upon moving the dresser 121 down, the chamber xe2x80x9caxe2x80x9d of the cylinder 132 is scarcely exhausted and thus the dresser 121 exhibits a discontinuous downward motion in a repetitive downward and stopping motions, cyclically.
The present invention has been made in the light of the problems described above, and an object thereof is to provide a polishing apparatus equipped with a light-load dresser capable of a precisely controlled light-load and achieving a smooth downward movement operation.
The present invention takes advantage of the mass of a dresser itself having a constant load in combination with a force provided by a single variable fluid pressure and thereby achieves precise control of the light load of the dresser.
That is, in order to solve the problems described above, the present invention provides a polishing apparatus comprising a turntable, a top ring and a dresser, each of which is rotatable independently, with an object to be polished being interposed between the turntable and the top ring so that a surface of the interposed object can be polished by a polishing cloth face defined on said turntable surface, wherein the polishing cloth face can be regenerated by compressing the dresser against the turntable, the apparatus characterized in that: a dresser unit including the dresser and a shaft for rotatably supporting the dresser is operatively mounted to a dresser supporting mechanism so as to be moved up and down freely with respect to the dresser supporting mechanism, and a push-up mechanism is installed between the dresser unit and said dresser supporting mechanism for pushing the dresser unit with an upward force, wherein a compression force applied by the dresser against the turntable can be adjusted by a balance between an own weight of the dresser unit itself and the upward force provided by the push-up mechanism. This upward force can be generated by a fluid pressure. Further, the shaft can be a driving shaft for rotationally driving the dresser.
Still further, the push-up mechanism may comprise: an elevating mechanism consisting of a piston-cylinder mechanism installed between the dresser unit and the dresser supporting mechanism; with a fluid supplying mechanism for supplying a fluid at a predetermined pressure level to the elevating mechanism, the fluid supplying mechanism supplying the fluid at the predetermined pressure level to one of the chambers within the cylinder divided by the piston of the elevating mechanism, while relieving the pressure in the other of the chambers so as to generate an upward force applied to the dresser unit.
Still further, the fluid supplying mechanism may comprise: a compressed fluid source connected to the one of the chambers of the cylinder of the elevating mechanism through a pipe; and a pressure control unit installed within the pipe for depressing the compressed fluid supplied from the compressed fluid source to the predetermined pressure level and supplying the depressed fluid to the one of the chambers of the cylinder.